3560 Port Channel

[sdawson35]

Okay so I have a 3560 (G model) and an HP DL380 file server, I want to create a port channel between to get higher throughput , Im not interested in redundancy just raw throughput.

So I configured Port 3 and Port 8 as Port Channel Group 1 and set the server NIC Teaming to automatic, this works but I dont get beyond a 1.0 Gb throughput, am I missing something ?

Do I need to use truly adjacent switch ports ? or am I missing something from my config ?

interface gigabitethernet0/3

switchport access vlan 2

switchport mode access

speed 1000

duplex full

channel-group 3 mode active

spanning-tree portfast

interface gigabitethernet0/8

switchport access vlan 2

switchport mode access

speed 1000

duplex full

channel-group 3 mode active

spanning-tree portfast

interface port-channel 3

switchport access vlan 2

switchport mode access

spanning tree-portfast

Regards

Scott.

[cpembleton]

Scott,

Putting 2 Gig links into a port-channel isn't just going to give you a true 2Gig link. 

The switch preforms hashing to determine which physical link to use for a given flow.  The hash can be mac,ip,or port based on src/dst or both.  So a single flow still won't be able to exceed 1Gig.  If you have multiple flows you could reach 2Gig utilization. 

To see your hashing being used run 'sh etherchannel load-balance'

Take a look at this link for some info on etherchannels.

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml#matrix

HTH

Chad

[sdawson35]

Oh Blast !.So to get throughput beyond a 1.0Gb I am going to need to change topology to fibre 2,4,6,8 Gbs or 10Gb copper/fibre.

Port channel only gives me redundancy and or load balacing , so now I am confused by HP's software telling me I can create a 2.0Gb pipe out of 2 1.0Gb links...maybe not via a Cisco product then ?

Regards

Scott.

[cpembleton]

It isn't a true load-balance.  That would be a marketing term not how it actually works. 

It's not packet1 uses link 1, packet 2 uses link2, packet3 uses link 1, etc...  Yes, you can get a combined 2G.  But it all depends on flows and hashing.  Say you have a server making a connection to storage that is attached to the etherchannel.  If the src/dst is the same that flow will always use the same link.  So the speed of the physical link is your limit.  If you have multiple unique flows you could then get a combined utilization up to the combined etherchannel speed. Although, Cisco's implmentation of hashing in the cat switches will have an unbalanced distribution.  Nexus stuff improves this to get a better balance among port members.   

LACP is a standard and it does have other aggregation options defined but Cisco only has the hashing described in doc. Don't know if other vendors implamented it different.  I know linux does. 

HTH

Chad

[Leo Laohoo]

The best way to describe etherchannel is like this:

Presume you have a two-link etherchannel to a server.  The server has, say, six packets.   The first two are normal size, packet three is three times the size of the first two.  Packet four, five and six are normal size.

So the switch sees the inbound packet one and two (one after another).  Since they are normal size and they "fit", they go down the "tube" in link one and link two of the etherchannel.  Packet three arrives so the switch tries to shove it down the link one.  While packet three is still going down link three, packets four, five and six arrives (one after another).  The switch sees that link one is "occupied" therefore the switch will send packets four into link two.  Packet four goes and the switch still sees link one occupied so the switch sends packet five down link two.

Finally packet three is gone so the switch decides to send the last packet down using link one.